What is the best font for extremely limited space, i.e. will fit the most READABLE text in the smallest space?

I often have very limited space when creating reports and dashboards for users. I usually use Arial, or Arial Narrow, but UI isn't my area of expertise, so I want to know, is there an optimal font for fitting the most readable text in the smallests space?

Here is an example. Keep in mind this is just an example, as there are many times that space is limited, such as when you need to squeeze a million columns into a report, etc.